1. Field of the Invention
The present invention relates to the field of electrical circuits. More particularly, the invention relates to amplifier circuits.
2. Background Art
Balanced amplifiers, such as balanced power amplifiers, which can be utilized in mobile communications devices, such as cell phones, as well as other types of electronic devices, can provide several advantages compared to single-ended amplifiers. Balanced amplifiers can provide, for example, improved input and output return loss, increased output power, improved third order intercept performance, and improved operational redundancy.
A balanced amplifier typically includes an isolated port termination resistor, which can absorb reflected power caused by an impedance mismatch between the output impedance of the balanced amplifier and the input impedance of a load, such as an antenna. However, if the reflected power becomes too large due to the mismatch between amplifier output impedance and load impedance, the isolated port termination resistor can be damaged or destroyed by a correspondingly large amount of power being dissipated in the termination resistor.
In a conventional approach, a large-size termination resistor can be coupled between the isolated port of the balanced amplifier and ground to prevent damage from high reflected power levels caused by a large mismatch between output impedance of the balanced amplifier and load impedance. However, a large-size termination resistor is undesirable for small-size balanced amplifiers, such as small-size balanced amplifiers typically utilized in cell phones as well as other mobile communications devices.